Nevertheless, when you have the binary, you stand a chance at reverse engineering. If you broadcast such a binary, you have a guaranteed leak. At least, when you don't publish at all, you stand a chance at actual secrecy. (Pretty unlikely, though, if too much people are involved.)
In software development, secrecy is often undesirable: nobody trusts you; nobody will work with you; nobody can help you - you are pretty screwed. Thus, all the OSS in the world's infrastructure these days.
http://blakemasters.tumblr.com/post/24464587112/peter-thiels-cs183-startup-class-17-deep-thought
Some perspectives on AI risk that might be interesting. Peter is (the primary?) donor for SI, and an investor in AGI startup Vicarious Systems.